Alexa, just to mention that Sainsburys takes payment for your shopping on the delivery day, not when you order (you mentioned two weeks). Since this last lockdown we've had weekly deliveries and been very impressed. To enable them to hold the delivery slot for you, you have to order at least £25 worth (don't hold me on the amount). I also start ordering two weeks ahead, and when the slots become available I order all the basics from my Favourites which amount to around £25 to reserve the slot, and then add, delete and tweak my order right up to the day before delivery.
I've been classified as clinically extremely vulnerable and have been messaged, emailed and had post from all the relevant organisations right from March 2020. My GP and hospital consultants have been fantastic and when I order regular prescriptions via PatientAccess, they are delivered to my home the following day. Very happy.